//Calculation.cs
class Calculation
{
public static void Calc()
{
// this is where i must see if the radioButton is Checked or Not, but it dosent see it from this Class...
if (ruletNumber / 2 == 0 && rdbEven.Checked == true)
{
//some code...
}
}

In which case you will have to change the method signature in your class like below. Also, I believe your condition ruletNumber / 2 == 0 should be ruletNumber % 2 == 0 since you are trying to check whether it's odd/even number